1. Field of the Invention
This invention relates to antiscalants having improved biodegradability. Such antiscalants are useful in a variety of applications, including boiling and cooling water scale prevention, desalination, struvite control and oilfield applications.
2. Description of the Related Art
Biodegradability of antiscale agents used in the oil and gas industry is of particular concern. See, e.g., S. Lewis and M. Szymanski, “Environmentally Acceptable Fluid-Loss Alternatives for Use in North Sea,” Fall 2004 SPE ATCE (Abstract). For example, Norway strongly favors the use of antiscale products for North Sea oil well applications that have relatively high biodegradability in seawater. Various test protocols for determining biodegradability are known, including the test method known as “Marine BODIS.” According to the “OSPAR Guidelines for Completing the Harmionised Offshore Chemical Notification Format (HOCNF) (Reference number: 2005-13), substances for which no biodegradation data are available shall be tested according to the standard test methods for biodegradability: OECD Guidelines for Testing of Chemicals, 1992, 306, or any of the four protocols published in the report “Biodegradability of chemicals in sea water. Results of a ring tests undertaken by OSPARCOM, were reported by Elf Akvamiljö, September 1996.” According to the United Kingdom Guidelines pertaining to the OSPAR Guidelines, the Marine BODIS method is one of the standard test methods. Biodegradability is also a concern in a variety of industrial applications outside of the oil and gas industry.
A number of polymeric antiscale agents are known. For example, U.S. Pat. Nos. 3,706,717; 3,879,288 and 4,518,511 disclose anionic polymers and methods of using them as antiscalants. However, the disclosed anionic polymers have relatively poor biodegradability. See also U.S. Pat. Nos. 5,064,563; 5,298,570; and 5,962,401. Anionic polymers carry a negative charge that is neutralized by positively charged counterions. The anionic polymer is generally considered to be the primary active ingredient in the polymeric antiscale agent, whereas the counterion is often regarded as a neutral or inactive species. Consequently, prior to the invention described below, relatively low molecular weight counterions such as sodium and potassium were generally considered desirable in order to maximize the active solids content of the antiscale agent and/or to minimize costs. Organic counterions such as alkylammonium species were generally considered undesirable because their relatively high molecular weights reduced the active solids content of the antiscale agent, and because of their relatively high costs as compared to counterions such as sodium and potassium.
There is a need for antiscale agents having improved biodegradability, as well as methods of improving the biodegradability of existing antiscale agents.